Recently, regulations obliging companies to store business documents and other data for a long period of time have been being strengthened. Storage apparatuses for storing files of such business documents and other data are required to have a function preventing alteration of data. In order to meet such a requirement, a file system having a WORM (Write Once Read Many) function (update prohibition function) is suggested.
Not only the function preventing alteration of data, but a function preventing deletion of files stored in a file system with the WORM function for a certain period of time (hereinafter sometimes referred to as the “retention period”) is also required. In order to meet this requirement, the file system with the WORM function often has a retention function (deletion prohibition function). In that case, processing for deleting the file system with the WORM function must be designed to normally terminate only after retention periods of all the files stored in the file system have expired.
Furthermore, a function capable of deleting even a file once stored in a storage apparatus with the WORM function under special circumstances, by exercising a privilege of doing so, is also required.
In Patent Literature 1, the WORM function and the retention function are realized by storing the ID and retention period of an object (file) to be stored in a volume (file system) in one entry in a table and referring to that table when updating and deleting the object.
When one or more files are transferred to a WORM file system according to Patent Literature 2, the WORM function and the retention function are realized by storing a retention period end date and time of a file in the furthest future from among the retention end dates and times of the files, as the retention period end date and time of the file system.